I agree that doing more has plenty of avantage, but is there something specifically about cooking?
Have you ever sew piece of clothes that you regularly wear? Most people never did... yet for something that will be used for hundreds of hours, we pay 20$+ for it instead of taking a few hours to do it. Why are we arguing about cooking ourself but not sewing our own clothes?
Cooking our own food is simply a tradition that stayed with us, nothing else. It doesn't make more sense to do it ourself, than making our own clothes.